This study will evaluate whether a drug called T-20 can slow or prevent a rapid return of HIV in the blood when HAART (highly active antiretroviral therapy) is stopped temporarily. HAART is a multi-dose regimen that is very effective in suppressing HIV and perhaps slowing or halting progression of the viral infection towards AIDS. However, this treatment is not problem-oriented. It cannot completely rid the body of virus, and long-term therapy carries a risk of toxicity (harmful side effects). Moreover, the treatment is difficult to adhere to because of the many pills and capsules that must be taken daily. When patients stop taking HAART, their viral levels climb again. This study will see if T-20 can prolong the time it takes for HIV blood levels to rise in patients who stop HAART temporarily. The results may provide insight into possible new HAART-sparing treatments.